Hot melt adhesive guns are known in which a cartridge of normally solid adhesive is inserted within a heated chamber of the gun, a portion of the cartridge being successively melted to provide a quantity of molten adhesive for dispensing from the gun nozzle. The rate at which a normally solid adhesive cartridge can be melted is governed by the diameter of the cartridge which confronts the heating surface in the gun chamber and by the operating temperature of the heating surface. To achieve a higher melting rate, a larger diameter cartridge can be employed for a given temperature but this would of course necessitate a gun of larger size and can result in a gun of unwieldy size to achieve certain high melting rates. The melting rate can be increased in a gun of smaller size by increasing the operating temperature, but higher temperatures can cause degradation of the adhesive composition. In addition, the higher temperature further lowers the viscosity of the molten adhesive and increases the likelihood of back flow of adhesive within the gun mechanism, with consequent contamination of the gun.
Heretofore, to satisfy the requirement for relatively large dispensing rates, typically greater than about 20 pounds of hot melt per day, bulk reservoir systems have been employed in which a heated tank containing a relatively large quantity of hot melt adhesive is coupled via a hose to a dispensing gun and molten adhesive pumped from the tank to the gun for dispensing. Such bulk systems in addition to being cumbersome are quite restrictive in use by reason of the attached bulky hoses. In addition, the hose often contains heaters to maintain the adhesive in liquid form, and flexing of the hose during use shortens the lifetime of the hose to an average of only about 4 or 5 months in typical installations. As a result, the maintenance cost of such bulk systems can be considerable. Moreover, the hose is usually plastic lined, which limits the permissable operating temperatures which can be employed without damage to the hose itself.